<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Hello World React</title>
</head>
<body>
  <div id="app">app</div>

  <script src="https://unpkg.com/react@16/umd/react.development.js" crossorigin></script>
  <script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js" crossorigin></script>
  <script src="https://unpkg.com/babel-standalone@6/babel.min.js" crossorigin></script>

  <script type="text/babel">
    
    class App extends React.Component {

      constructor() {
        super()
        this.state = {
          message: 'Hello World'
        }
      }

      render() {
        return (
          <div>
            <h2>{this.state.message}</h2>
            <button onClick={this.btnClick.bind(this)}>改变文本</button>
          </div>
        )
      }

      btnClick() {
        // this.message = 'Hello React'
        this.setState({
          message: this.state.message === 'Hello World' ? 'Hello React' : 'Hello World'
        })
      }
    }

    ReactDOM.render(
      <App />,
      document.getElementById('app')
    )
  </script>
</body>
</html>